FIG. 16 is a compositional diagram of a conventional ballasted track which uses cross-sleepers. In the diagram, 4 is a rail, 6 is ballast, 7 is a rail fastening, and 8 is a cross-sleeper. Conventional ballasted tracks have a structure wherein the track frame is comprised of mono-block or twin-block cross-sleepers 8 which are placed transversely with respect to the rails. The train load and the loads in the longitudinal direction of the rails and in the transverse direction of the rails are supported by the beating pressure and friction of the ballast 6.
The above-mentioned conventional tracks using cross-sleepers have a tendency to form track irregularities since they are subjected to the severe effect of repeated train loads. As a result, such irregularities increase the severity of train vibrations, deteriorating the running stability and the ride comfort. For this reason, maintenance work is regularly required to accurately measure the condition of track irregularity, and to align or repair the places where track irregularities are formed, whenever such repair is needed.
However, the required labor and expenses are enormous, not only because such maintenance and repair are still dependent upon manual labor, but especially because such work is often done at night and needs to be completed within a short time. Furthermore, labor shortages and the aging of such maintenance workers have become problems. Therefore, a track structure is desired which can reduce the amount of required maintenance work.
With conventional tracks using cross-sleepers, not only does the ballast pressure become large in localized areas due to the intermittent support provided to the rails, but also the repeated loads with respect to the wheels due to the passage of trains form track irregularities. When these track irregularities become large, the severity of the train vibrations increase, and the running stability and ride comfort deteriorate. For this reason, there is the problem that regular maintenance work is required.
Additionally, French Patent No. 76-22586 teaches the use of short sleepers which are placed parallel to the rails. Even with these types of sleepers, however, solutions are still necessary to problems such as how to maintain the track geometry, and how to make the ballast pressure uniform along the longitudinal direction of the rails.
The ladder-type sleepers of the present invention are offered as a solution to the above-mentioned problems. These ladder-type sleepers aim to reduce the amount of maintenance work required by (1) decreasing track irregularities due to repeated train loads by improving the distribution of the train load, and (2) decreasing track irregularities due to loads in the transverse direction of the rails, such as lateral thrust, by taking advantage of the high transverse resistance provided by continuous longitudinal sleepers. A further objective of the ladder-type sleepers of the present invention is the presentation of a railway track made by coupling these sleepers to rails. By adopting a continuous beam structure in the direction parallel to the rails, and by placing continuous rail pads which continuously support the rails, the ladder-type sleepers of the present invention make it possible to reduce ground vibrations, rolling noise, and corrugation of the rails.